Inflatable safety systems for motor vehicles have undergone significant development efforts in recent years due in part to an increased awareness as to their effectiveness. These inflatable safety systems are typically activated upon receipt of a signal from an appropriate detector or sensor which indicates that inflation of the confinement is required. A variety of inflators are used by these systems to expand the confinement in a manner which provides certain advantages. Many systems initiate inflation by "removing" an isolation between the confinement and the inflator. Thereafter, some inflating medium, whether it be pressurized gases, gases generated by combustion of a propellant, a mixture thereof, or other suitable fluids, is supplied to the confinement.
A portion of the development efforts for inflatable safety systems have concentrated upon or at least addressed controlling the flow from the inflator to the confinement after inflation has been initiated. In order to provide a reliable inflatable safety system, not only must there be a sufficient flow of the inflating medium to the confinement in a timely manner, but the confinement itself must remain structurally intact throughout operation. One proposed alternative for achieving these two fundamental objectives concentrates on the material selection for various components of the inflator.
U.S. Pat. No. 3,567,245 to Ekstrom, issued Mar. 2, 1971, discloses utilizing certain materials for the barrier which provides the initial isolation between the inflator and the confinement. In one embodiment, the isolating barrier is a friable or fragmentable material which is disintegrated or comminuted by the activation of an explosive device positioned therewithin to initiate inflation. The resultant materials, which are apparently of a sufficiently small size, are then forced through various passageways by the exiting pressurized fluid used for inflation and thus presumably enter the confinement. The utilization of an elastomeric material, particularly an RTV rubber, in this type of configuration is also suggested since the resultant materials allegedly do not damage the confinement due to their resiliency. Another embodiment includes an isolating barrier having preformed grooves thereon such that when the explosive device is activated, the barrier breaks into sections defined by the grooves. These resultant sections are able to pass through the passageways so as to not block the flow of fluid to the confinement, and thus also presumably enter the confinement.
U.S. Pat. No. 3,900,211 to Russell et al., issued Aug. 19, 1975, discloses selecting an appropriate material for the component used to release a poppet to initiate inflation. Generally, a poppet is positioned in a discharge conduit connected to a source of pressurized fluid to initially prohibit flow therefrom. A support tube assists in maintaining the poppet in this closed position and also separates the poppet from a pyrotechnic charge. Upon receiving a signal that inflation is required, the pyrotechnic charge is activated to disintegrate the supporting structure. The pressure exerted on the face of the poppet by the stored fluid thereafter moves the poppet to expose a discharge outlet to initiate the flow. Due to the positioning of the support tube between the poppet and the pyrotechnic charge and the travel of the poppet toward the charge after the activation thereof, the disclosure indicates that there is no expulsion of support tube or pyrotechnic residue in the fluid stream.
In recognition that fragments or other foreign materials generated upon activation of the inflator may enter into the flow and adversely affect the overall performance of the inflatable safety system, such as by restricting the flow rate through blocking passageways to the confinement or by damaging the confinement when propelled against the interior surfaces thereof, filtering-type devices were incorporated to remove these fragments and other foreign materials. U.S. Pat. Nos. 3,618,980 to Leising et al., issued Nov. 9, 1971; U.S. Pat. No. 3,822,895 to Ochiai, issued Jul. 9, 1974; and U.S. Pat. No. 4,114,924 to Kasagi et al., issued Sep. 19, 1978, are representative of these efforts. Leising et al. discloses in one embodiment the positioning of a vane structure between a propellant chamber and an inflatable bag. When a collision is sensed and the propellant within the propellant chamber is ignited, the by-products thereof flow through the vane structure. Heavier particles are thrust outwardly by the vanes and are directed to a trap where they are retained until converted into a gas or until the bag is inflated. However, the gases generated by the burning of the propellant flow to the confinement. In another embodiment, a screen structure is used to prevent molten liquid masses of propellant from entering into the inflatable bag while allowing gases to pass through alternate passageways.
Ochiai discloses a filtering apparatus positioned in the discharge area of a receptacle containing a source of an inflating gas. A cup-shaped barrier, having a convex side which faces the stored gas and a concave side which contains a rupture inducing means, initially contains the gas within the receptacle. When the cup-shaped barrier is ruptured, gas flows through the filter and to the gas bag. However, the broken pieces of the cup-shaped barrier are prevented from entering the gas bag by the filter.
Kasagi et al. discloses positioning a collecting chamber between an inflator and an inflatable safety bag to collect fragments or pieces generated by the removal of the initial isolating structure between the inflator and the inflatable bag. More particularly, the collecting chamber is positioned near a bent portion (illustrated as a 90.degree. bend) of the conduit connecting the inflator and bag in substantial alignment with the conduit prior to making the bend. Consequently, as the gas and any fragments generated by removal of the isolating barrier approach the collecting chamber, the inertial forces possessed by the heavier fragments direct them to continue into the aligned collecting chamber where they are trapped while the gases flow around the bend in the conduit and are directed to the inflatable bag. Various other embodiments address structural modifications of the collecting chamber and/or the conduit, as well as the positioning of certain collecting materials within the collecting chamber.
The above-described filtering-type devices for controlling flow from the inflator to the confinement suffer from a number of deficiencies. For instance, filtering or collecting devices may not retain all of the particles generated upon activation of the inflator. Consequently, some particles may pass through the filtering device and become lodged in a passageway to restrict the flow to the confinement or some may enter the confinement, both of which may adversely affect performance of the inflatable safety system. Even if the filtering device properly functions and retains all of the generated particles, this may in and of itself introduce a further flow restriction to the confinement by blocking an entire passageway or a portion thereof. Furthermore, these filtering-type devices also add to the material and subsequent maintenance costs of the inflator.
As a result of the above deficiencies with systems which address controlling flow by concentrating on the by-products generated by the removal of the isolation between the inflator and the confinement, recent efforts have begun to utilize methods of initiating inflation which reduce the quantity of activation by-products. One possible alternative is the use of a projectile to "remove" the isolating member.
Representative of punching-type projectiles include U S. Pat. Nos. 3,788,667 to Vancil, issued Jan. 29, 1974, and U.S. Pat. No. 3,869,143 to Merrell, issued Mar. 4, 1975, which generally disclose the use of a ramming, piston-like member to remove a barrier isolating the inflator from the confinement after an appropriate signal is received by the respective activating apparatus. These barriers have grooves formed thereon to provide predetermined break lines such that when the ramming member impacts the barrier, the barrier is completely removed from its supporting structure to initiate inflation.
French Patent No. 2,557,251, issued Jun. 28, 1985, discloses releasing a fluid under pressure by using a projectile. More particularly, a plurality of metal particles (i.e., lead shot) are directed to and "burst" a cup-shaped diaphragm to release the pressurized fluid. Not only does there not appear to be a mechanism for trapping the lead shot after having been fired (i.e., the lead shot may restrict flow by collecting in a passageway and/or may enter the confinement to which the source is connected), but it does not appear that the referenced "bursting" of the disk by the disclosure would indicate any desire to reduce the amount of byproducts generated upon activation.
U.S. Pat. No. 3,836,170 to Grosch et al., issued Sep. 17, 1974, generally discloses a variety of projectiles for initiating inflation. In one embodiment, a piston-like ramming member is used to remove the isolating barrier which has rupture lines placed thereon and is therefore similar to that disclosed by Vancil and Merrell discussed above. In another embodiment, a cylindrically-shaped projectile positioned in a tubular guide is directed toward the isolating barrier by the activation of a pyrotechnic charge. A trap positioned beyond the barrier collects the projectile, the by-products of the activation of the pyrotechnic charge, and presumably portions of the isolating barrier, all of which allegedly do not impede the flow of gas through the plurality of exiting passageways. Another embodiment utilizes a blunt nosed projectile (i.e., one which tapers to a degree but not to a point) and an isolating barrier which appears from the drawings to be dished out on the downstream side of the projectile which is exposed to a portion of the source of compressed gas. When the blunt-nosed projectile impacts the dished out barrier on its substantially planar side, the barrier is allegedly torn in a star-shaped manner and the projectile and other by-products of activation are caught in a trap so that the flow of gas is not impeded. Although the blunt-nosed projectile embodiment is alleged to produce a star-shaped tear in the isolating barrier, this particular design would not produce a consistent tear-pattern on the barrier. Initially, it would appear that a portion of the barrier, coinciding essentially with the area of the blunt-nosed face of the projectile, would be "punched out" by the impact of the projectile and become completely separated from other portions of the barrier. However, assuming no punched out portion is produced, the potential for portions of the barrier breaking off and entering the flow still exists. Although thee is no explicit disclosure as to the type of surface forming the tapered portion of the projectile, it appears from the drawings that this surface is smooth. Consequently, this surface would not cut or otherwise separate the barrier in a predetermined manner as it passed therethrough, but instead the barrier would tear along lines dictated, in part, by the stresses in the barrier.
As a general rule of manufacturing processes, the thickness of a piece of metal stock determines, in part, the radius of a bend which may be formed without cracking or shearing the stock in the region of the bend. When the radius of a bend in a piece of stock becomes less than the initial thickness thereof, the potential for the development of cracks in the bend or the shearing of the stock in this region increases. Consequently, when it is desirable to achieve a cutting action in this region, the stock may be "bent" at a radius which is less than the thickness thereof, and preferably at a radius which is significantly less than the thickness to ensure shearing or cutting takes place in this region.
Assuming that the blunt-nosed projectile configuration of Grosch et al. would not completely punch out any portion of the isolating barrier, the smooth surface over the tapered portion of the projectile would, based upon the foregoing, bend versus cut the barrier as it passed therethrough since there is no disclosed "edge" which would cause a controlled cut or shear (i.e., the radius of the tapered surface is not, from the drawings, less than the thickness of the isolating barrier). The resultant bending of the barrier by the penetrating projectile would therefore cause the barrier to "tear" along lines dependent upon, in part, the existing stresses in the barrier. Therefore, the separation of the barrier by the blunt-nosed projectile configuration of Grosch et al. is not controlled (i.e., the pattern for the tearing will typically vary dependent upon various factors), thereby creating the potential for separating the barrier in a manner which would result in portions thereof breaking off and entering the flow.
French Patent Nos. 1,147,005, issued Nov. 18, 1957, and 2,543,658, issued Oct. 5, 1984, each generally disclose a projectile for releasing a pressurized fluid from a container. The disclosed projectiles taper to a point and appear to be continuously smooth over the entire tapered surface. The apparent smoothness of the tapered portions of the projectile would also produce inconsistent and uncontrolled results in "removing" or separating a barrier as discussed above due to the resultant bending of the barrier (based upon the radius of the tapered portion) and subsequent uncontrolled "tearing" of the barrier along lines dependent, in part, upon the stresses therewithin. In fact, French Patent No. 2,543,658 discloses that the projectile utilized therein actually "shatters" the isolation which would generate and introduce numerous particles into the system, and thus does not even recognize the desirability of controlling the amount of byproducts generated by separation of the barrier.
Canadian Patent No. 967,192, issued May 6, 1975, discloses another projectile head design for releasing a compressed gas. A spring loaded plunger extends through a bottle of compressed gas. When a collision is sensed, the plunger is driven through the diaphragm which isolates the compressed gas from the inflatable member to release the gas. The end of the plunger appears to have a series of unjoined (i.e., non-intersecting), inclined planar surfaces which, although tapered, do not appear to taper to a point. The resultant projectile is thus of the blunt-nosed configuration utilized by Grosch et al. which suffers from the above-noted deficiencies. Moreover, it is not apparent from the drawings and the disclosure does not appear to indicate that this projectile head configuration would cut an isolating member in a consistent manner to reduce fragmentation. Since the inclined faces of the projectile do not intersect, the edges formed by the inclined faces would bend versus cut the barrier, due to the radius of the edge in relation to the diaphragm, resulting in the type of inconsistent and uncontrolled "tearing" of the diaphragm as addressed above.